This invention relates to vegetation cutting apparatus, more particularly to the type of vegetation cutting apparatus which cuts by using one or more rapidly moving lines extending from a rotating housing.
The advantages, including safety and flexibility, offered by this type of vegatation cutting apparatus over the type of apparatus using blades or comparable cutting mechanisms, is well appreciated. Thus, improving and overcoming problems in this former type of apparatus are goals which have received a great deal of attention. Two areas of significant concern have been the development of the line that is required and the development of mechanisms for storing and dispensing additional line as the line breaks or wears out due to its cutting action or due to the heat and fatigue which develop as a result of the interactions between the line and other parts of the apparatus.
However, and perhaps somewhat surprisingly, the area which has most stubbornly resisted satisfying solutions is the design of structure through which the line can exit a housing rotating at, e.g. between approximately 5000-7000 rpms, while avoiding excessive heating and breakage.
The history of this concern and of the continuing attempts to satisfy it over the years is well documented in the literature and in the marketplace. Thus, early approaches to trimmer apparatus, as in U.S. Pat. Nos. 3,708,967, 3,826,068, and 3,859,776, focus on curvilinear cutting head surfaces with the lines loosely disposed therebetween, elastomeric line retainers to hold the line against a surface, or pins which the lines may contact.
Subsequent approaches incorporated in trimmer apparatus include interconnected or distinct metal inserts to curve along at least part of a curvilinear wall of the cutting head, as in U.S. Pat. Nos. 4,052,789, 4,124,938, and 4,114,269, along with a spool extension extending into the exit port, as in U.S. Pat. No. 4,052,789. Alternative subsequent approaches incorporate arcuate structures extending into exit channels from both sides to hold the lines, elastomeric retainers to hold the lines against arcuate structures having metal inserts therein, and the more traditional curvilinear surfaces with the lines therebetween, one of such surfaces being provided with a metal insert, as in U.S. Pat. Nos. 4,035,912, 4,067,108 and 4,104,797. Also application Ser. No. 742,963, with Virgil H. Stair and Dale D. Evenson as inventors, discloses support structure for the lines exterior to a spool cavity, which, as indicated therein, may have metallic surfaces for conductivity purposes.
Apparatus more closely resembling traditional lawn mowers, but employing rapidly moving cutting lines, evidences somewhat similar problems and concerns. Thus, U.S. Pat. No. 4,054,992 discloses rather tightly-fitting exit channels through a disc-like member, into which the lines are press-fit; U.S. Pat. No. 4,112,653 discloses, in most relevant part, structures creating tightly-fitting passageways about the lines and also creating curvilinear wall surfaces; and U.S. Pat. No. 4,107,901 discloses line-supporting tubes near the periphery of lawn mower-type structure. U.S. Pat. No. 4,136,446 is also of some interest.
The most trying condition for the exit structure is where the rotation is rapid, e.g. of the order of 6500-7000 rpms. Such rapid rotation is often associated with heavy cutting needs and with the use of larger size lines to withstand the larger forces associated with such cutting needs. Thus, certain designs have proven satisfactory for lighter tasks, but have failed in the heavier, more difficult situations. A typical example of this, which is presented in somewhat more detail below, is shown in FIG. 4.
The developments evidenced by the foregoing patents, and an appreciation of the effects of the high speeds involved in apparatus of the type of concern herein, ultimately makes quite understandable the difficulties encountered in designing a satisfactory exit structure and the criticality of refinements to the attainment thereof.